Different technologies are known for visualizing a vascular system of the human or animal body. In a form of digital subtraction angiography (DSA), after administration of a contrast agent two-dimensional projection images are acquired repeatedly at a predetermined, fixed projection angle by an X-ray apparatus, a reference image (e.g., mask image) is subtracted from each image. During the procedure, the mask image is generated at a point in time at which no contrast agent is present. In this way, the arrival of the contrast agent in the vessels, and so the blood flow, may be visualized (e.g., perfusion). Owing to the subtraction of the individual time-series images from the mask image, the visualizations from now on contain only the vessels filled with contrast agent. The background (e.g., tissue, bone, air) is suppressed. Digital subtraction angiography plays a major role in diagnostics, for example, in the detection of pathological vascular diseases in the brain.
A tool by the name of Syngo iFlow is known that generates a parametric visualization of the arrival time of a contrast agent bolus based on digital subtraction angiography. The individual images of the DSA series (e.g., time-series images) are combined into a parametric image in which the arrival time of the contrast agent bolus may be visualized in color-coded form. In this case, the arrival time is, for example, the time up until the contrast agent reaches its maximum intensity; a so-called time-to-peak map (TTP map) is produced. An early arrival time of the contrast agent may be represented, for example, in a color from the red color spectrum, and a late arrival time in a color from the green or blue color spectrum. More information on this may be found in the publication titled “syngo iFlow/Dynamic Flow Evaluation/Answers for life” published by Siemens AG, Medical Solutions, Angiography, Fluoroscopic and Radiographic Systems.
In many cases, only the (e.g., smaller) vessels of the parenchyma (e.g., tissue) are of interest in the angiographic images, in digital subtraction angiography, for example, although the vessels are often obscured to a great degree by the large affarent and/or efferent vessels (e.g., arteries, veins). Currently, however, it is not possible to eliminate the large vessels from the projection images obtained by digital subtraction angiography.
In addition to conventional two-dimensional subtraction angiography, imaging techniques are known that enable a three-dimensional visualization of a vascular system or of the blood flow, referred to as 3D angiography or 3D perfusion. Computed tomography (CT angiography, perfusion CT), magnetic resonance tomography (magnetic resonance angiography, magnetic resonance perfusion imaging) as well as C-arm-based imaging may be cited here by way of example. Basically, these three-dimensional techniques may also apply the subtraction principle, thus enabling pure vessel visualizations to be generated while suppressing the background. With the three-dimensional techniques, it is known to segment large vessels, (e.g., to classify them as such and where necessary to remove them from the visualization). The use of three-dimensional techniques during a treatment, however, is subject to restrictions and the temporal resolution is poorer than in the case of the 2D techniques.